Optical system for forming a windowed web in a color cathode ray tubescreen structure

ABSTRACT

An improvement is provided in the optical system utilized for photo-forming the multiple window pattern defined by the opaque interstitial web portion of a CRT composite screen structure. Exposure illumination from an elongated primary light source is selectively modified by a composite light attenuation coating of nonsymmetrical density discretely disposed relative to the lens in the pattern exposure system. The vapor disposed coating is heavier in the generic form of a modified lemniscate which selectively modifies the photo exposure to effect a variable gradient of window sizes from center to edge of the screen and additionally provides windows of a substantially equal size in annular orientation progressively about the central axis of the screen.

United States Patent Ng et al. [451 June 6, 1972 [54] OPTICAL SYSTEM FOR FORIVIING A WINDOWED WEB IN A COLOR Primary Examiner-Samuel S. Matthews CATHODE RAY TUBESCREEN Assistant Examiner-Robert P. Greiner AttorneyNorman J. OMalley, Donald R. Castle and STRUCTURE Frederick H. Rinn [72] Inventors: David M. Ng; Charles H. Rehkope, both of Seneca Falls,'N.Y. [57] ABSTRACT [73] Assignee: Sylvania Electric Products, Inc. An improvement is provided in the optical system utilized for photo-forming the multiple window pattern defined by the [22] f 1970 opaque interstitial web portion of a CRT composite screen [21] Appl. No.: 86,123 structure. Exposure illumination from an elongated primary light source is selectively modified by a composite light at- I tenuation coating of nonsymmetrical density discretely [52] US. Cl ..95/l dis posed relatlve to the lens in the pattern exposure system. 2; 9 Q The vapor disposed coating is heavier in the generic form of a l 1 ie 0 arc modified lemniscate which selectively modifies the photo posure to effect a variable gradient of window sizes from [56] References cued center to edge of the screen and additionally provides win- UNITED STATES PATENTS dows of a substantially equal size in annular orientation progressively about the central axis of the screen. 3,448,667 6/1969 Smithgall ..95/l

4/1934 Eich ..355/83 X 12 Claims, 10 Drawing Figures PATENTEDJun s 1912' sum 1 OF 4 T INVENTORS FRI-OR AR DAVID M. N6 8.

CHARLES H. REH KOPF BY PATENTEDJUN s 1912 SHEET 2 OF 4 "INVENTORS .DAVID M. NG & CHARLES H. REHKOPF BY ATTOZN EX LIV TRANSMISSION PAIENIEDJUM 6 I972 uv TRANSMISSION (PERCENT) (PERCENT) SIIEEI 30F 4 :DIAMETR'ICAL' LENS DIMENSION ALONG Y AXIS I I IIIIIIII 1.5 'I.O .5 O .5 L0 1.5 2.0 2.5

(INCHES) I I I I I I I I I O 1' "2.5 "2.0 L5 --LO "-5 O .5 L0 (.5 2.0 2.5

DIAMETIZICAL LENS DIMENSION ALONG X AXIS (INCHES) I PATENTEnJuu 6 m2 3. 667, 355

- sum u or 4 EXPOSURE LIGHT INTENSITY RATIO (PERIPHERY TO CENTER) NEGATIVE i, po s mve l l l l I -2.0 -|.O 0 L0 2.0 3-0 4.0 v

SCREEN WINDOW -'D\AME.TER GRADIENT (UN/7'5 /A M/LS) (camera To PERIPHERY) 1 OPTICAL SYSTEM FOR FORMING A'wmnownn WEB m A coLoR CATHODE RAY TUBFscREEN STRUCTURE cRoss REFERENCE o RELATED APPLICATION Thisapplication contains matter disclosed but not claimed in a related US. Pat. application filed concurrently herewith and assigned to the assignee of the present invention. This related application is Ser. No. 86,030 filed Nov. 2, I970, now abandoned titled Means and Process For Achieving A Controlled Gradient Density Coating On A Light Attenuation Medium.- I n 1 BACKGROUND OF THEINVENTION d This invention relates to cathode .ray tubes and more particularly to an improved optical system utilized for photoforming the multiple window pattem in the opaque interstitial web portion of a color cathode ray tube composite screen structure. 1

Cathode ray. tubes capable of presenting multi-color display imagery, such as those utilized in color television applications, conventionally employ patterned screens which are comprised of an orderly array of separate color fields formed of repetitive groups of related hue-emitting phosphor materials. These screen pattern groupings are normally disposed as stripes, or dots depending upon the type of color tube structure under consideration. As an example, in the well-known shadow mask type of tube construction, the color screen pattern is conventionally made up of a'vast multitude of discrete dots formed of selected cathodoluminescent phosphors which are usually arranged in triad relationship. Such dot'supon selective electron excitation, emit predetermined additive primary hues to produce the desired color imagery. By some screen forming techniques, the individual phosphor dots comprising the screen pattern are ofien in substantially tangential contact with one another; while by other screenforming procedures, the individual dots are separated by relativelysmall interstitial spacings which enhance color purity by reducing the possibility of undesirable electron excitation of adjacent dots. Associated with the dot type of screen within the tube envelope, is a foraminous structure or shadow mask having multitudinous apertures therein. Each of these apertures is-related to a specific grouping or triad of dotscomprising the color screen pattern, and spaced therefrom in a manner to enable the selected electron beams, traversing theapertures, to impinge the proper dots therebeneath. I

To enhancecolor purity, improve brightness and accentuate contrast of the color screen image, an advantageous composite screen structure has been developed, wherein a dotdefining interstitial spacing is provided between the individual dots in the form-of an opaque light-absorbing material. In essence, each of the phosphor dotscomprising the screen pattern is encircled or defined by a substantially dark interstitial encompassment which collectively forms a multi-opening pattern or windowed webbing having "substantially opaque interstitial connections. This opaque interstitial encompassment of the color-emitting dots provides a safety factor to enhance color purity and visual contrast in the display. Thus, to achieve desired results, it is imperative that these definitive windows be of. proper sizes and in precise orientation with reference to the individual phosphor dots at the areas of respective beam impingement. H

To provide an image display embodying equal energy white requires a mixture of hues embodying the three additive primary color emissions having substantially related intensities.

Accordingly, in any particulararea' of the composite screen structure, the tri-dot definitive windows should be of predeterminately related sizes.

Fabrication of the windowed interstitial webbing is accomplished either before or after phosphor screening by several processes wherein photo-deposition techniques play a prominent role. The exposure devices and associated optical systems employed in fabrication of the windows resemble those utilized in phosphor dot formation. Conventionally,

these include an exposure light source and lens oriented in a manner to provide light optics intended to substantially duplicate the electron optics of the operating tube. It has been found that the optical preciseness necesary for fabricating the desired window pattern of the composite screen structure is not inherently available in the usual phosphor screening expo sure systems. This lack of optical precision is sometimes evidenced by the non-uniformity of the electron-excited white 1 field in various portions of the windowed screen in an operating tube. As an example, an excited screen exhibiting a 9,300 K white temperature in the center may present off-white fields in several separate peripheral areas of the screen. For instance, in substantially the l to 2 o'clock region the white may exhibit a cyan tinge; in substantially the 5-to-7 o'clock region, a yellow tinge; and in substantially the lO-to-l 1 o'clock area, a pink tinge. Such off-white areas are found to be due to a subtractive' effect produced by a difference in the desired size of one of the related tii-dot windows, i.e., red, blue, or green, in the respective areas. The smaller sized window also aggravates 'misregistration or eclipsing of the impinging beam by a portion of the opaque interstitial material defining the window which adds to the undesirable ofi-white efle'ct.

Prior to the use of a definitively windowed screen structure, the ratio' of color emitted from a screen of uniform density, to produce a desired white, was controlled -by the respective beam currents and a respective mask aperture common for each triad. The contiguously related phosphor dots associated therewith were of relatively large areas. With the introduction of the composite screen, the phosphor defining windows therein also became important determinant factors influencing the contrast, brightness and color quality of the excited screen area. This emphasizes the fact that advancement in the art of producing improved color-cathoderay tubes brings with it an imperative need for improved precision and refinement in screen fabrication means and techniques. 7

OBJECTS AND SUMMARY OF INVENTION It is an object of the invention to reduce'the aforementioned disadvantages and to provide an improvement in the optical system utilized in photo-forming the windowed web of the composite screen structure. Another object is the provision of light attenuation means of a predetermined non-uniform pattern and density for use in the optical system to provide exposure illumination for effecting substantially constant window sizes for all three colors in annular orientation 'pro'gressively'about the central 'axis of the screen, and provide a variable gradient of window sizes in a radial direction from center to edge of the screen structure.

The definition of density as used herein refers to the opaque quality of the coating.

The foregoing objects are achieved in one aspect of the invention by an improvement in the opticalsystem for photoforming the multiple window pattern of the opaque interstitial web of a composite color cathode ray tube screen structure. ll-

lumination from an elongated primary exposure light source is selectively attenuated by a composite light attenuation coating, of a differential non-symmetrical density, disposed relative to a surface of the lens to discretely afiect the exposure illurninau'on passing therethrough. The composite attenuation coating which affects the utilized area of the lens imparting differential translucency thereto, is disposed as first and second related patterns having coating densities gradually decreasing from center to peripherylThe second pattern is of heavier graduated density and exhibits the generic form of a modified lemniscate whereof substantially equi-sized lobe portions are disposed on either side of the center plane of the lens which also includes the lens Y axis. The heavier deposition of the second pattern coating afiects substantially the lens central and transverse regions which are related to the X axis thereof. The elongated exposure illumination is so modified by the related differential coatings, to effect a variable gradient of window diameters from center to periphery 'of the screen, I

and additionally produces substantially constant window sizes in annular orientation progressively about the central axis of the screen. The resultant improved window pattern provides enhanced contrast, brightness and color purity in the finished composite screen.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a sectional view of a color cathode ray tube of the shadow mask type'employing a windowed composite screen and plural electron beams;

FIG. 2 is a'plan view of a prior art rectangular composite screen showing windows and respective beam landings;

FIG. 3 is a plan view of an exposure apparatus employing an embodiment of the optical system of the invention for photoforming the multiple window portion of the composite screen structure;

FIG. 4 is a plan view of the coated'lens taken along the line 4-4 of FIG. 3.

FIG. 5 is a profile representation of the UV transmission of the composite attenuation coating on the surface of the lens taken along the line 5of FIG. 4

FIG. 6 is a profile of the UV transmission of the composite attenuation coating taken along the line 6-6 of FIG. 4;

FIG. 7 is a plan view looking down through the panel alon the plane 77 of FIG. 3;

FIG. 8 is a graph illustrating the relationship between exposure light intensity and screen window diameter gradient; and

' FIGS. 9 and 10 are cross-sectional views showing other embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings.

With reference to the drawings, there is shown in FIG. 1 a conventional shadow mask type of color cathode ray tube 11 having a central axis 13 therethrough. Suitably positioned within the neck portion 14 of the envelope 15 are three electron emitters or guns 17 oriented, for example, substantially 120 apart and equally spaced about'the central axis 13 to provide a delta arrangement of electron beams 19, 20 and 21, respectively. Coil means in the form of yoke 23, positioned externally on the tube, are utilized to deflect the respective electron beams over the raster area; The several beams are directed to converge at the apertured shadow mask 25, and thence pass through the apertures 27 therein to discretely impinge the composite screen structure 29 spaced therebeneath. The composite screen 29, which is disposed on the interior surface of the viewing panel 31, comprises a multiple window pattern 33 formed of an opaque interstitial webbing 35 that discretely defines the multitudinous window areas 37. Disposed relative to the window areas 37 are a multitude of triadically arranged dots 39 of red, blue, and green color-emitting electron responsive phosphor materials. While a tri-gun shadow mask color tube is illustrated in FIG. 1, it is not intended to be limited thereto, as the invention to be described is also applicable in other types of image reproduction devices utilizing plural beams of radiant energy excitation.

Since the tube axis, and panel axis are substantially coincidental, it seems expedient for clarification to denote these respective axes as the central axis 13.

. From the viewpoint of an observer 41, facing the front of the view panel 31, the phosphor areas available for utilization in forming the visible display, on the composite screen 29, are determined by the respective areas of the defining windows 37 in the interstitial webbing 35. The geometry of the tube 11 is such that the three electron beam landings form a substantially triadical formation on the'screen. To adequately utilize the beam landings, the respective phosphor window area 37 should coin'cide therewith. As previously mentioned, such was not always true especially when the optical system conventionally utilized for phosphor dot exposure was used for window'fabncation. A resultant difference in window size areas was evidenced in certain portions of the screen. This condition was particularly noticeable in tubes having wide angles of deflection, such as in excess of 70, for instance deflection in rectangular screen tubes. Such is illustrated in FIG. '2 wherein a prior art rectangular screen 43 is shown from the viewpoint of an observer facing the viewing panel 31. Illustrative groupings of windows and'beam landings are shown in exaggerated size. Representative of the axial window groupings 45 is the triad of area related windows 46, 47, and 48 with the defining interstitial webbing indicated at 49. When the electron beams 19, 20, and 21 pass through the mask aperture and make landings in the respective window areas, they desirably impinge upon the respective green (G), red (R) and blueemitting (B) phosphor materials disposed therein.'Due to sizegraduated apertures in the mask 25 and photo-forming exposure, sizes of the window diameters progressively change by a predetermined gradient from the center 13 of the screen to the periphery 30 thereof. Such is evidenced, for example, by the triadical window groupings 51 and 77 which are substantially of like transverse annular orientation K with reference to the central axis 13. It is desired that the windows associated with each color pattern, in annular orientation progressively from the center 13, be of substantially constant size, but such is not always achieved, as evidenced by the smaller blue-associated window 75 in grouping 77, a condition which will be further considered subsequently. Another example is noted in the upper left portion of the screen in substantially the 10 to ll oclock region 53, which is further removed from the central axis 13, the illustrated peripheral grouping 55 showsthe green windows 57in that region to be smaller in size than the associated red and blue windows 59 and 61. Consequently, the interstitial webbing 58 defining the green windows is more extensive. This smaller size green window 57 is a deterrent to achieving the desired white color temperature in that area of the screen, causing a pink tinge to be evidenced thereat. Since the smaller window approaches the area of the respec tive impinging beam, a slight misplacement of the window 57 will cause the electron beam 19 to be partially eclipsed by the surrounding opaque webbing which further decreases the amount of available green illumination. A'similar situation may exist in the upper right area of the screen in substantially the l to 2 oclock region 63 where an'exemplary peripheral triad grouping of windows 65 exhibits a red window 67 of smaller area. These decreased red window areas decreases the red component in that region of the screen thereby degrading the white color temperature by effecting a cyan tinge thereat. Eclipsing of the beam by the opaque interstitial webbing 69 may further aggravate this condition. As previously mentioned, the screen area in substantially the 5 to 7 oclock region 71 may likewise exhibit a degraded white temperature due to smaller blue window areas 75 in the triadical window groupings 77 in that region. The resultant reduction of the blue emission component effects a yellow tinge thereat.

It has been found that the respective aforementioned smaller window areas can be increased as desired to equal or be proportional to the other window areas in the respective triadical groupings. This is accomplished by incorporating an improvement in the optical system employed in photo-forming of the multiple window pattern. The improvement is in the form of related light attenuation coating patterns of differential nonsymmetrical density that are disposed relative to the lens in the system to discretely effect the exposure illumination passing therethrough. This provides a variable gradient of screen window sizes .from center to edgeof the screen and effects substantially constant window sizes in annular orientation progressively about the central axis 13.

Optical exposure means, such as that shown in FIG. 3, is employed to photo-form the multiple window pattern of the opaque interstitial web of a composite color cathode ray tube screen structure. The basic features of the optical system are similar to those disclosed in US. 'Pat. No. 3,509,802, issued to G. A. Burdick and assigned to the same assignee as the present invention. Another related optical system is disclosed in US. Pat. No. 3,448,667 issued to H. E. Smithgall and assigned to the same assignee as the present invention.

Prior to the exposure of each of the respective window patterns, the inner surface of the viewing panel 31 is coated with a light hardenable photosensitive substance81 such as dichromate sensitized polyvinyl alcohol. The apertured shadow mask 25 is temporarily positioned in spaced adjacency with the sensitized panel, whereupon the mated mask-panel assembly is positioned on the exposure apparatus 83. Within the apparatus, there aremeans 85 for predeterminately positioning an optical system 87 comprising: a primary source of exposure illumination 89, an associated light source collector rod 93, a modified plano-concave lens 95, and a two pattern composite light attenuation coating 97 disposed relative to a surface of said lens 95. For purposes of illustration, the profile of the composite lens coating 97 is exaggerated in FIG. 3. Actually, the composite coating is of substantially neutral density, for example, a thin vapor disposed metallic coating of a suitable metal or alloy having varied thickness and exhibiting discrete degrees of opacity. Nickel-chromium alloys, such as'lnconel, which is available from the International Nickel Company, Inc., New York, New York, have been found suitable for this usage. Since the index of refraction of the thin deposit is nowhere near that of glass, its refractive interference pattern is considered minimal. a

. In the light exposure procedure, discrete areas ofthe coated panel are subjected to light radiated from the primary light source 89 which is attenuated by the coating 97, refracted by the lens 95, and directed through the mask apertures 27. The discrete areas of the photosensitive coating 81 which receive the exposure light radiation are light polymerized or hardened and adhere to the inner surface of the panel 31 forming a first pattern of the subsequent window area. With the shadow mask still in place, the above-described procedure is twice repeated to dispose each of the related two remaining window patterns making up the triadical groupings. For the separate exposure of each of the respective window patterns, the optical system 87 is shifted substantially 120 about the central axis 13.

In observing the screen from the exterior of the viewing panel 31 as shown in FIG. 7, several orientation designations or transversals are considered. Conventionally, the screen area is divided into four quadrants usually referenced through the central axis 13 and defined by the 12-6 oclock minor screen axis AH and the 3-9 oclock major screen axis LM. In counter-clockwise order, the 12-3 oclock portion defines the first screen quadrant, the 9-12 oclock area the second quadrant, the 6-9 oclock portion the third quadrant and the 3-6 oclock area the fourth quadrant. Two other screen designations in the form of additional orientation transversals, also reference through the central axis 13, are denoted as the 2-8 o'clock screen diagonal EF and the 4-10 oclock diagonal CD respectively.

With particular reference to FIGS. 3 through 7, the optical system 87 and improvements therein are illustrated in greater detail. The apparent origin of the exposure light appears to follow a locus due to the refraction of the light by the lens 95.

Light emanating from the collector rod 93, as for example attenuated rays represented by lines 101 and 103, ultimately reach the photosensitized coating 81 to photo-form like peripheral window areas 105 and 107, respectively; they being diagonally opposite areas of the screen. Due to the refraction of the lens 95, the light rays 105 and 107 appear to originate at point 0. Point P designates the apparent light source for ray 109 beamed to the screen center window area ll'lfThus, the apparent locus of motion of the light source falls along the line 0-1. The optical system 87 is designed to provide deposition of the window pattern a manner that the respective electron beams in the operating tube will impinge thereinto. Since the windows of eachtriadical grouping will be subsequently associated with green, red, or blue emitting phosphors, the window pattern areas are identified as g, r, and b respectively, and may be separately formed in any order. As described in this specification, the window areas are slightly larger than the areas of the impinging beams, but such is not to be considered limiting. The optical system shown is utilized in photo-forming each of the three like window patterns. A first of the patterns is, for example, the array of fg associated windows, one of which is denoted as 105 in substantially the upper left portion of the second screen quadrant and one of similar relationship at 107 in substantially the'lower right portion of the fourth screen quadrant.

The improved optical system of the invention may be used, for example, in photo-fomiing the window pattern of the composite screen structure of a 25-inch rectangular tube having substantially 90-degree deflection. Looking into the viewing panel 31 positioned atop the exposure apparatus 83, details and positioning planes, utilized in orienting the optical system 87 for photo-disposing the several related window patterns, are indicated. As illustrated, the exemplary position of the optical system 87 for forming the g associated windows, is substantially in the plane CD. This plane substantially corresponds to the 4-10 oclock screen diagonal which is removed clockwise from the 12-6 oclock minor screen axis in the ordinate plane AH by 120. The optical system, having an axis 113, which is laterally offset from the central axis 13 by the distance k, incorporates therein a primary exposure light source 89 in the form of an elongated luminous arc emanating between the electrode 115 and 116 in a mercury vapor lamp 117. An example of a conventional lamp is type BH6 which emits a high value of UV radiant energy in the- 300-400 nanometer (nm) range. The primary light source 89 has a longitudinal axis 119 that is oriented substantially normal to the optical system axis 113. The light collector 93 is a conduit means such as a quartz rod which collects and transfers, by internal reflections, a portion of the non-symmetrical radiant energy produced by the source 89. Even though a substantially concave-shaped reflector 121 is utilized, the exposure radiant energy emanating from the terminal end 123 of collector rod 93 is substantially of an elongated pattern. Since the intensity of the exposure illumination varies as the inverse square of the distance between the source and point of 'exposure, discrete compensation is required to attain annular unifomiity of light intensity from the non-symmetrical light source. To expedite clarity, details of this light attenuating coating are omitted in FIG. 7.

To compensate for the non-symmetrical pattern of illumination, a discretely fonned composite light attenuation coating 97 is disposed relative to a surface of the lens 95 in a manner to affect the exposure light transmitted therethrough. As illustrated in FIGS. 3, 4, and 7, the composite light attenuation coating 97 is disposed in substantially the form of two related patterns directly on the surface of the lens 95, as, for example, by vapor deposition, but such deposition and surface containment are not to be considered limiting, as other techniques of formation and other related surfaces are in keeping with the invention. Since the structure and detailed orientation of the lens 95 do not substantially influence the desired functioning of the discretely disposed coating 97, specific details of the lens construction are eliminated fromthis specification and drawings relating thereto. The lens 95 has Xand Y axes and a center plane therethrough substantially coincident with the Y axis and normal to the plane of the X and Y axes. The lens95 is oriented in'the optical system with its X axis substantially parallel with the longitudinal axis 119 of the elongated light source 89, and the Y axis is substantially in the plane of the CD diagonal. The composite light attenuation coating 97 on the planar surface 99 of the lens 95, substantially covers the whole of that surface in a differential density deposition of two related coating patterns. Considered as a whole, the composite attenuation pattern exhibiting differential translucency has been determined through extensive experimentau'on to achieve the desired compensation for the non-symmetrical illumination emitted by the elongated source. Since the lens 95 is of high UV transmissive optical glass, the UV attenuation of the glass per se is of very low order, and is considered minimal in this instance. The window exposure illumination provided by the improved optical system 87 so oriented, produces exposure control to particularly modify or effect the g associated windows, in substantially the upper left screen area 53, that should be of a desired size relative to that of the other windows in the triadical groupings thereat.

I ,In greater detail, the first attenuation pattern of the composite coating 97 is comprised of substantially two parts 126, '126' which affect primarily the Y axis region of the lens 95. The density of this coating pattern decreases in a gradual manner from the central region of the lens to the periphery thereof. The related second attenuating pattern of the composite coating 97 is generally of a gradual heavier density than that exhibited by the first pattern, and is in substantially the generic form of a modified lemniscate 127. The major dimension W of this lemniscate formation is oriented substantially in the lens transverseregion related to the X axis thereof. The minor dimension Z is oriented across the waist section 135 of the lemniscate substantially coincident with the Y axis of the lens 95. The heaviest or most opaque coating deposit of this second attenuation pattern 127 is substantially in the central area 129 of the lens 95 in the general region intersected by the axis of the optical system 113 with the density decreasing gradually outward therefrom to the periphery 130. This lemniscate coating formation 127 is formed on the lens 95 with substantially equisized lobe portions 131 and 133 disposed on either side of the center plane 125. The areas of heaviest coat ing density of the first attenuating pattern 126, 126' are adjacent the waist section 135 of the modified lemniscate formation 127.

With reference to FIG. 5, there is shown a profile 137 of the UV transmission of the composite attenuation coating 97 as evaluated relative to the center plane 125 along the Y axis of the lens 95 which, in this instance, has a inch diameter. As portrayed, disregarding the reflective factor of the glass, the differential ultraviolet transmission of the coating per se ranges from substantially 98 percent at the periphery 130 of the lens to substantially 16 percent in the center lemniscate area 129. The waist 135 of the lemniscate formation of coating 127 is evidenced as extending from substantially from 0.4 to +0.8 inches of the diametrical lens dimension. Similarly, FIG. 6 illustrates a UV transmission profile of the same composite attenuation coating 97 relative to the X axis of the same lens 95 as shown in-FIG.5. Across the lens on this axis, the differential UV transmission of the coating increases from-substantially 98 percent at the periphery of the lens to substantially 16 percent in the central area 129. In this profile the expanse of greater attenuation in the lemniscate formation of coating 127 is evidenced with relationship to the major dimension W thereof as extending from substantially l.0 to +1.0 inches of the diametrical lens dimension.

It has been found that a foraminous shadow mask 25 exhibiting a positive aperture gradient, i.e., whereof the apertures 27 are sequentially graded from larger diameters in the central area to smaller diameters at the peripheral region, can be utilized to produce a multiple windowed screen structure 33 having a negative window gradient whereof the respective triad oriented windows are sequentially graded in an annular manner from smaller dimensioned windows in the central area of the screen to larger dimensioned windows at the peripheral region hereof. To achieve this relationship, the graduated composite attenuation coating 97, comprising the first and second related attenuation patterns, increases in density from the periphery to the center of the lens 95, with the greatest density of attenuation coating being disposed in the central area 129 of the lens to provide thereat substantially less than percent UV light transmission therethrough.

It has also been discovered that a shadow mask having the aforementioned positive aperture gradient, can also be utilized to produce a multiple windowed screen structure 33 wherein the windows exhibit a positive window gradient, i.e., the respective triad oriented windows are sequentially graded in an annular manner from larger dimensioned windows in the central area of the screen to smaller dimensioned windows at the peripheral region thereof. To accomplish this dimensional relationship, the graduated composite attenuation coating 97 has decreased density in the central portion 129 to provide thereat more than substantially 20 percent UV light transmission therethrough. It has been found that other factors, such as, temperature, humidity and coating sensitivity and thickness are also contributing determinants, so that the aforementioned approximate 20 percent pivotal value for window gradient changeover may vary, for example, by about 3:2.0 percent.

Reference is made to FIG. 8 wherein the relationship of exposure light to screen window diameter gradient is shown. The required exposure light intensity ratio is determined by the distribution of the composite light attenuation coating 97. For example, to obtain a negative window gradient as aforedescn'bed, i.e., smaller windows in the center than at the periphery of screen structure, the composite attenuation coating 97 should provide a light transmission ratio of at least about 2:1 from periphery to center. It has been found that the aforementioned approximate 20 percent center transmission appears to fulfill this requirement. If a positive windowdiameter gradient is desired, a decreased density of center lens coating is required which in turn permits higher center light transmission and results in a lower light intensity'ratio of less than approximately 2: l. I

Other embodiments of the optical system are shown in FIGS. 9 and 10. For example, in FIG..9, a light permeable planar medium 147, such as a thin plate of optical quality glass, is spacedly positioned intermediate the lens 149 and the terminal end 151 of the collector rod 153 within the optical system positioning means 155. The composite attenuation coating 157, while shown as being disposed on the under surface of the plate 147, can be disposed on the upper surface as well. In the FIG. 10 embodiment, a light permeable planar medium 147', in the form of an optical plate, is positioned intermediate the lens 149' and the mask by the optical system positioning means 155'. The composite attenuation coating 157', which is applied to the under surface of plate .147, can be disposed on the upper surface if desired. In each of the embodiments shown in FIGS. 9 and l0,'necessary compensation for the conjunctive refractive characteristics of the associated lens and respective plates are adequately resolved by appropriate modification of the lens contour. I

As previously mentioned, light reflection values have been factored out of the coating attenuation values. Actually, the lens and optical plate surfaces, not covered by subject light attenuation coating, are usually covered with a micro-thin antireflective coating such as, for example, a quarter wave magnesium fluoride film.

In photo-disposing a second of the three related window patterns, such as for example, the r" associated windows, the optical system 87 is positioned along the plane EF which substantially corresponds to the 28 o'clock screen diagonal,

being removed clockwise from' the 12 o'clock position by 240. In FIG. 7, the whole optical system is shifted to coincide with the plane EF. For purposes of clarity, only the light source collector rod is indicated at 93a. The window exposure illumination emanating from the improved optical system so positioned provides exposure control to effect r associated windows in substantially the upper right screen area 63, that,

are of a size related to that of the other windows in the triadical groupings thereat.

For deposition of the third of 12" associated windows, the improved optical system 87 is oriented in the AH or minor axis plane wherein light source collector rod 93b is indicated. With the optical system so positioned, exposure improvement falls mainly within the 5 to 7 oclock screen area 71 to provide 3" windows of desired size. It is noted that thisaffected portion of the rectangular screen is not as large as it would be in a round screen 161.

After the three respective window patterns are thus exposed and polymerized-the shadow mask 25 is removed and the exposed coating 81 suitably developed to remove the web-like unpolymerized interstitial area. This development step provides a polymerized window pattern in the format of multitudinous polymerized areas surrounded by a connected web pattern of substantially bare glass. Following development, the patterned panel isovercoated with an opaque colloidal suspension ofv graphite, and then treated with an appropriate degrading agent and rinse to effect removal of the polymerized window fpattern format. This degradation and removal of the polymerized window areas also loosens and removes theassociated graphite which is disposed thereon. Thus, thereis'produced an opaque interstitial web having multitudinous windows therein in the form of discretely defined barejglass areas. It is on these window areas that the respective color-emitting phosphor materials are conventionally disposed by techniques known to the art.

Thus, there is provided a windowed color cathode ray tube screen structure that manifests accentuated contrast, improved brightness and enhanced color purity. Such ad'- vantages are provided by employing theaforedescribed improved optical system in photo-forming the windowed web of the composite screen structure. The composite light attenuation coating employed in the improved optical system provides exposure illumination that effects substantially constant window sizes for all three colors in annular orientation progressively about thecentral axis of the screen, and additionally provides a variable gradient of window sizes in a radial direction from center to periphery of the screen structure.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein withoutdeparting from the scope of the invention as defined by the appended claims. i

l. Animprovement in an optical-system for photo-forming the multiple window pattern of the opaque interstitial web of a composite color cathode ray tube screen structure on a screen bearing surface having a forarninous mask spacedly related thereto and a central axis therethrough to provide a variable gradient of screen window sizes from center to edge of said screen andeffect substantially constant window sizes in annutoward the periphery of said related lens.

lar orientation progressively about said central axis, said optical system having an axis and incorporating therealong a primary elongated source of .exposure illumination having a longitudinal axis oriented substantially normal tosaid system axis in a manner to emit substantially nonsymmetrical illumination relative to the axis of said system, an associated light source collector rod, and a lens having transverse X and Y axes with'a center plane therethrough, said optical system being positioned in a manner to direct light emanating from said collector rod through said forarninous mask to photo-dispose the multiple window pattern of said interstitial web on said screenbearing surface,,said improvement comprising:

a composite light attenuation coating of differential nonsymmetrical density discretely vapor disposed in first and second related and predetennined patterns relative to a surface of said lens in a manner to affect the light transmitted by the lens portion utilized for the passage of exposure illumination therethrough, said lens being oriented in said optical system with its'X- axis substantially parallel with thelongitudinal axis of said elongated light source, said first vapor-disposed attenuation coating pattern having a differential density affecting primarily the Y axis region of said lens in a gradually decreasing manner, from the central region of said lens' to the periphery thereof, said second vapor-disposed attenuation coating pattern being in general-of heavier differential density than said first pattern and being in the substantially generic form of a modified lemniscate having a major dimension oriented in the lens transverse region related primarily to the X axis thereof and a minor dimension substantially coincident with the related Y axis of said lens, said I lemniscate formation having a waist section with substantially equi-sized lobe portions on either side of said center plane including the related Y axis of said lens, said related attenuation patterns of differentially vapor-disposed coating providing control of the exposure illuminationto effect a predetennined variable gradient of window diameters from center to edge in said interstitial screen pattern and provide windows of substantially constant size in annular orientation progressively about the central axis of the composite screen structure. 1 2. The improved optical system according to claim 1 wherein the greatest attenuation density of said composite vapor-disposed coating patterns is relative to substantiallythe central area of said related lens and diminishes differentially in a gradual and selective nonsymmetrical manner therefrom toward the peripheral regionof said related lens.

3. The improved optical system according to claim I wherein the greatest attenuation density of said first vapordisposed coating patternis substantially adjacent said waist section of said lemniscate formation and diminishes 'differentially in a predetermined gradual nonsymmetrical manner therefrom toward the peripheral region of said related lens. v

4. The improved optical system according to claim .1 wherein the greatest attenuation density of said second vapordisposed coating pattern is substantially in the central region of said lemniscate formation and diminishes differentially in a predetermined gradual nonsymmetrical manner therefrom 5. An improved optical system according to claim 1 wherein the forarninous mask exhibits. a positive aperture gradient whereof the apertures are. sequentially graded 'from larger in the central area to smaller at the peripheral region, and wherein said vapor-disposed composite attenuation coating gradient of said predetermined relatedattenuation patterns increases in density from periphery to center of said related lens with the greatest attenuation density in said central area thereof providing less than substantially 20 percent of light transmission therethrough to efiect a negative window gradient whereof the size related triad oriented windows are sequentially graded in an annular manner from smaller dimensioned windows in the central area of the screen to larger dimensioned windows at the peripheral region thereof.

6. An improved optical system according to claim 1 wherein the forarninous mask exhibits a positive aperture gradient whereof the apertures are sequentially graded from larger in the central area to smaller at the peripheral region and wherein said vapor-disposedcompositeattenuation coating.

gradient of said related predetermined attenuation patterns increases in density from periphery to center of said lens with the attenuation density in said central area thereof providing size related triad oriented windows are sequentially graded in an annular mariner from larger dimensioned windows in the central area of the screen to smaller dimensional windows at the peripheral region thereof.

7. A substantially translucent optical component utilized in conjunction with an exposure light source in an optical system I for photo-forming the multiple window ,pattem of the opaque interstitial web portion of a composite color cathode ray tube screen structure on a screen bearing surface, said component comprising:

a substantially transparent glass medium having X and Y transverse axes and two oppositely related surfaces positioned between said light source and said screen bearing surface; and i v a light attenuation coating of differential nonsymmetrical density discretely vapor disposed in predetermined first and second related patterns on a surface of said glass medium, said first vapor-disposed attenuation coating pattern having a differential density affecting primarily the Y axis region of said medium in a gradually decreas' ing manner from the central region to the periphery thereof, said second vapor-disposed attenuation coating pattern being in general of heavier differential density than said first pattern and being in the substantially generic form of a modified lemniscate having a major dimension oriented in the lens transverse region related primarily to the X axis thereof and a minor dimension substantially coincident with the Y axis of said medium, said lemniscate formation having a waist section with substantially equi-sized lobe portions on either side of said Y axis.

8, The substantially translucent optical component according to claim 7 wherein the greatest attenuation density of said composite vapor-disposed coating patterns is relative to substantially the central area of said component and diminishes differentially in a gradual and selective nonsymmetrical manner therefrom toward the peripheral region of said component.

9. The substantially translucent optical component according to claim 7 wherein the greatest attenuation density of said first vapor-disposed coating pattern is substantially adjacent the waist section of said lemniscate formation and diminishes differentially in a gradual and selective nonsyrnmetrical manner therefrom toward the peripheral region of said component.

10. The substantially translucent optical component according to claim 7 wherein the greatest attenuation density of said second vapor-disposed coating pattern is substantially in the central region of said lemniscate formation and diminishes differentially in a gradual and selective nonsyrnmetrical manner therefrom toward the peripheral region of said component.

11. The substantially translucent optical component according to claim 7 wherein the composite vapor-disposed attenuation coating gradient of said predetermined related attenuation patterns increase in density from periphery to center of said component with the greatest attenuation density in the central area thereof provides less than substantially 20 percent of light transmission therethrough. 7

12. The substantially translucent optical component according to claim 7 wherein the composite vapor-disposed attenuation coating gradient of said predetermined related attenuation patterns increases in density from periphery to center of said component with the attenuation density in the central area thereof providing more than substantially 20 percent of light transmission therethrough.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORECTION YP t' i- 'ti'Nb I Dated June 6,

inventor) David-M. Ng and Charles 'Rehkopf It is' certified 'that'error appears in the above-identified patent and that said Letters Patent areyhereby corrected 'as shown below:-

Front Page, second inventor name should head Rehkopf v- Col. 1, lines 8 and 9 'how abandoned" should read now U.S. Patent No. 3,664,295

a C01 1-, line .9 v "and-Process" should be deleted. I V I Signeddand sealedthis 22nd day of May 1973.

(SEAL) Attes't:

EDWARD M. FLETCHER,JR. ROBERT 3OTTSCHALK I Attesting Officer Clommissloner of Patents 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 'N o. 3,667,355 Dated June 6, 1972 Inventor) David-M. Ng and Charles H. Rehkopf It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Front Page, second inventor name should bead Rehkopf Col. 1, lines 8 and 9 "'now abandoned" should read now U.S. Patent No. 3,664,295

' Col. l-, line. 9 "and Process" should be deleted. I I

Signed, and sealed this 22nd day of May 1973.

(SEAL) Attest:

EDWARD M FLETCHER,JR. ROBERT @OTTSCHALK Commissloner of Patents' Attesting Officer 

1. An improvement in an optical system for photo-forming the multiple window pattern of the opaque interstitial web of a composite color cathode ray tube screen structure on a screen bearing surface having a foraminous mask spacedly related thereto and a central axis therethrough to provide a variable gradient of screen window sizes from center to edge of said screen and effect substantially constant window sizes in annular orientation progressively about said central axis, said optical system having an axis and incorporating therealong a primary elongated source of exposure illumination having a longitudinal axis oriented substantially normal to said system axis in a manner to emit substantially nonsymmetrical illumination relative to the axis of said system, an associated light source collector rod, and a lens having transverse X and Y axes with a center plane therethrough, said optical system being positioned in a manner to direct light emanating from said collector rod through said foraminous mask to photo-dispose the multiple window pattern of said interstitial web on said screen-bearing surface, said improvement comprising: a composite light attenuation coating of differential nonsymmetrical density discretely vapor disposed in first and second related and predetermined patterns relative to a surface of said lens in a manner to affect the light transmitted by the lens portion utilized for the passage of exposure illumination therethrough, said lens being oriented in said optical system with its X axis substantially parallel with the longitudinal axis of said elongated light source, said first vapor-disposed attenuation coating pattern having a differential density affecting primarily the Y axis region of said lens in a gradually decreasing manner, from the central region of said lens to the periphery thereof, said second vapor-disposed attenuation coating pattern being in general of hEavier differential density than said first pattern and being in the substantially generic form of a modified lemniscate having a major dimension oriented in the lens transverse region related primarily to the X axis thereof and a minor dimension substantially coincident with the related Y axis of said lens, said lemniscate formation having a waist section with substantially equi-sized lobe portions on either side of said center plane including the related Y axis of said lens, said related attenuation patterns of differentially vapor-disposed coating providing control of the exposure illumination to effect a predetermined variable gradient of window diameters from center to edge in said interstitial screen pattern and provide windows of substantially constant size in annular orientation progressively about the central axis of the composite screen structure.
 2. The improved optical system according to claim 1 wherein the greatest attenuation density of said composite vapor-disposed coating patterns is relative to substantially the central area of said related lens and diminishes differentially in a gradual and selective nonsymmetrical manner therefrom toward the peripheral region of said related lens.
 3. The improved optical system according to claim 1 wherein the greatest attenuation density of said first vapor-disposed coating pattern is substantially adjacent said waist section of said lemniscate formation and diminishes differentially in a predetermined gradual nonsymmetrical manner therefrom toward the peripheral region of said related lens.
 4. The improved optical system according to claim 1 wherein the greatest attenuation density of said second vapor-disposed coating pattern is substantially in the central region of said lemniscate formation and diminishes differentially in a predetermined gradual nonsymmetrical manner therefrom toward the periphery of said related lens.
 5. An improved optical system according to claim 1 wherein the foraminous mask exhibits a positive aperture gradient whereof the apertures are sequentially graded from larger in the central area to smaller at the peripheral region, and wherein said vapor-disposed composite attenuation coating gradient of said predetermined related attenuation patterns increases in density from periphery to center of said related lens with the greatest attenuation density in said central area thereof providing less than substantially 20 percent of light transmission therethrough to effect a negative window gradient whereof the size related triad oriented windows are sequentially graded in an annular manner from smaller dimensioned windows in the central area of the screen to larger dimensioned windows at the peripheral region thereof.
 6. An improved optical system according to claim 1 wherein the foraminous mask exhibits a positive aperture gradient whereof the apertures are sequentially graded from larger in the central area to smaller at the peripheral region and wherein said vapor-disposed composite attenuation coating gradient of said related predetermined attenuation patterns increases in density from periphery to center of said lens with the attenuation density in said central area thereof providing more than substantially 20 percent of light transmission therethrough to effect a positive window gradient whereof the size related triad oriented windows are sequentially graded in an annular manner from larger dimensioned windows in the central area of the screen to smaller dimensional windows at the peripheral region thereof.
 7. A substantially translucent optical component utilized in conjunction with an exposure light source in an optical system for photo-forming the multiple window pattern of the opaque interstitial web portion of a composite color cathode ray tube screen structure on a screen bearing surface, said component comprising: a substantially transparent glass medium having X and Y transverse axes and two oppositely related surfaces positioned between said lIght source and said screen bearing surface; and a light attenuation coating of differential nonsymmetrical density discretely vapor disposed in predetermined first and second related patterns on a surface of said glass medium, said first vapor-disposed attenuation coating pattern having a differential density affecting primarily the Y axis region of said medium in a gradually decreasing manner from the central region to the periphery thereof, said second vapor-disposed attenuation coating pattern being in general of heavier differential density than said first pattern and being in the substantially generic form of a modified lemniscate having a major dimension oriented in the lens transverse region related primarily to the X axis thereof and a minor dimension substantially coincident with the Y axis of said medium, said lemniscate formation having a waist section with substantially equi-sized lobe portions on either side of said Y axis.
 8. The substantially translucent optical component according to claim 7 wherein the greatest attenuation density of said composite vapor-disposed coating patterns is relative to substantially the central area of said component and diminishes differentially in a gradual and selective nonsymmetrical manner therefrom toward the peripheral region of said component.
 9. The substantially translucent optical component according to claim 7 wherein the greatest attenuation density of said first vapor-disposed coating pattern is substantially adjacent the waist section of said lemniscate formation and diminishes differentially in a gradual and selective nonsymmetrical manner therefrom toward the peripheral region of said component.
 10. The substantially translucent optical component according to claim 7 wherein the greatest attenuation density of said second vapor-disposed coating pattern is substantially in the central region of said lemniscate formation and diminishes differentially in a gradual and selective nonsymmetrical manner therefrom toward the peripheral region of said component.
 11. The substantially translucent optical component according to claim 7 wherein the composite vapor-disposed attenuation coating gradient of said predetermined related attenuation patterns increase in density from periphery to center of said component with the greatest attenuation density in the central area thereof provides less than substantially 20 percent of light transmission therethrough.
 12. The substantially translucent optical component according to claim 7 wherein the composite vapor-disposed attenuation coating gradient of said predetermined related attenuation patterns increases in density from periphery to center of said component with the attenuation density in the central area thereof providing more than substantially 20 percent of light transmission therethrough. 